U.S. patent application number 12/514942 was filed with the patent office on 2011-01-20 for absorbent articles comprising acidic cellulosic fibers and an organic zinc salt.
This patent application is currently assigned to SCA Hygiene Products AB. Invention is credited to Linus Fredlinger, sa Lindstrom, Madeleine Pehrson, Jan Petrusson, Jan Wastlund-Karlsson.
Application Number | 20110015596 12/514942 |
Document ID | / |
Family ID | 38220856 |
Filed Date | 2011-01-20 |
United States Patent
Application |
20110015596 |
Kind Code |
A1 |
Wastlund-Karlsson; Jan ; et
al. |
January 20, 2011 |
ABSORBENT ARTICLES COMPRISING ACIDIC CELLULOSIC FIBERS AND AN
ORGANIC ZINC SALT
Abstract
An absorbent article, such as a diaper, panty diaper, sanitary
napkin or incontinence device includes a liquid-permeable topsheet,
a backsheet and an absorbent core enclosed between the
liquid-permeable topsheet and the backsheet. The absorbent core
includes acidic fluff pulp having a pH of 5.5 or less and an
organic zinc salt, in particular zinc ricinoleate. The combination
of organic zinc salt and acidic fluff pulp exerts a synergetic
effect in the suppression of ammonia.
Inventors: |
Wastlund-Karlsson; Jan;
(Molndal, SE) ; Petrusson; Jan; (Goteborg, SE)
; Pehrson; Madeleine; (Molnlycke, SE) ; Lindstrom;
sa; (Goteborg, SE) ; Fredlinger; Linus;
(Kungsbacka, SE) |
Correspondence
Address: |
BUCHANAN, INGERSOLL & ROONEY PC
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Assignee: |
SCA Hygiene Products AB
Goteborg
SE
|
Family ID: |
38220856 |
Appl. No.: |
12/514942 |
Filed: |
November 17, 2006 |
PCT Filed: |
November 17, 2006 |
PCT NO: |
PCT/EP06/11066 |
371 Date: |
May 14, 2009 |
Current U.S.
Class: |
604/359 ;
536/101; 604/367; 604/375 |
Current CPC
Class: |
A61L 15/28 20130101;
A61L 15/18 20130101 |
Class at
Publication: |
604/359 ;
604/367; 604/375; 536/101 |
International
Class: |
A61L 15/46 20060101
A61L015/46; A61F 13/53 20060101 A61F013/53; A61L 15/20 20060101
A61L015/20; C08B 15/05 20060101 C08B015/05 |
Claims
1. Absorbent article comprising a liquid-permeable topsheet, a
backsheet and an absorbent core enclosed between said
liquid-permeable topsheet and said backsheet, wherein said
absorbent core comprises acidic cellulosic fibers having a pH value
of 5.5 or less, and an organic zinc salt.
2. Absorbent article according to claim 1, wherein said cellulosic
fibers are fluff pulp fibers.
3. Absorbent article according to claim 1, wherein the acidic
cellulosic fibers comprised in the absorbent core are obtained by
acidifying cellulosic fibers with an acidifying agent.
4. Absorbent article according to claim 3, wherein the acidifying
agent is an organic acid having a pK value of at least 1.5
(measured in water at 25.degree. C.).
5. Absorbent article according to claim 3, wherein the acidifying
agent is selected from aqueous solutions of citric acid, oxalic
acid, lactic acid, malic acid, malonic acid, maleic acid, succinic
acid, tartaric acid, sorbic acid, formic acid, salts thereof, and
mixtures thereof.
6. Absorbent article according to claim 1, wherein the acidic fluff
pulp has a pH value of 5.0 or less.
7. Absorbent article according to claim 1, wherein the acidic fluff
pulp has a pH value of 2.0 to 5.0.
8. Absorbent article according to claim 1, wherein the amount of
organic zinc salt is at least 10.sup.-5 g Zn per g dry acidic
cellulosic fibers.
9. Absorbent article according to claim 1, obtained by treating the
absorbent core or the acidic cellulosic fibers contained therein
with a solution of the organic zinc salt.
10. Absorbent article according to claim 1, wherein the organic
zinc salt is selected from zinc salts of carboxylic acids having 2
to 30 carbon atoms.
11. Absorbent article according to claim 10, wherein the carboxylic
acid represents an unsaturated hydroxylated fatty acid having 8 to
18 carbon atoms.
12. Absorbent article according to claim 10, wherein the zinc salt
is zinc ricinoleate.
13. Absorbent article according to claim 1, wherein the backsheet
is liquid-impermeable.
14. Acidic cellulosic fibers having a pH of 5.5 or less, comprising
a zinc salt of a monocarboxylic acid.
15. Acidic cellulosic fibers according to claim 14, wherein said
monocarboxylic acid represents an unsaturated hydroxylated fatty
acid having 8 to 18 carbon atoms.
16. Acidic cellulosic fibers according to claim 14, wherein said
organic zinc salt is zinc ricinoleate.
17. Acidic cellulosic fibers according to claim 14, obtained by
treating cellulosic fibers with an acidifying agent and the zinc
salt of a monocarboxylic acid.
18. Acidic cellulosic fibers according to claim 14, wherein said
acidifying agent is selected among organic acids having a pK value
(water, 25.degree. C.) of at least 1.5.
19. Acidic cellulosic fibers according to claim 18, wherein said
acidifying agent is present in an amount of 1 to 20 wt. % based on
the dry weight of the untreated fibers.
20. Acidic cellulosic fibers according to claim 14, wherein the
cellulosic fibers are fluff pulp fibers.
21. A method for controlling odour comprising utilizing the acidic
cellulosic fibers according to claim 14.
22. A method according to claim 21 comprising controlling odour in
absorbent articles.
23. Absorbent article according to claim 1, wherein the absorbent
article is a diaper, panty diaper, sanitary napkin or incontinence
device.
24. Absorbent article according to claim 1, wherein the acidic
fluff pulp has a pH value of 3.0 to 4.0.
Description
[0001] The present invention relates to an absorbent article such
as a diaper, panty diaper, sanitary napkin or incontinence device,
which comprises an effective odour control system, and
odour-controlling cellulosic fibers which can be used in such
absorbent articles. The present invention relates in particular to
such absorbent articles wherein acidic cellulosic fibers, such as
acidic fluff pulp having a pH 5.5 or less, and an organic zinc salt
such a zinc ricinoleate interact favorably, in particular
synergetically to reduce malodours such as ammonia.
TECHNICAL BACKGROUND
[0002] One important area of development in the area of absorbent
articles of the above-mentioned type is the control of odourous
compounds forming typically after the release of body fluids,
especially over a longer period of time. These compounds include
fatty acids, ammonia, amines, sulphur-containing compounds and
ketones and aldehydes. They are present as natural ingredients of
body fluids or result from degradation processes of natural
ingredients such as urea, which is broken down by microorganisms or
bacteria occurring in the urogenital flora to ammonia.
[0003] Various approaches exist to suppress the formation of
unpleasant odours in absorbent articles. WO 97/46188, WO 97/46190,
WO 97/46192, WO 97/46193, WO 97/46195 and WO 97/46196 teach for
instance the incorporation of odour inhibiting additives or
deodorants such as zeolites and silica. The absorption of bodily
liquids reduces however the odour inhibiting capacity of zeolites
as soon as these become saturated with water, as mentioned for
instance in WO 98/17239.
[0004] A second approach involves the addition of lactobacilli with
the intention of inhibiting malodour-forming bacteria in the
product. The incorporation of lactobacilli and their favourable
effect are disclosed for instance in SE 9703669-3, SE 9502588-8, WO
92/13577, SE 9801951-6 and SE 9804390-4.
[0005] Moreover, it is known from WO 98/57677, WO 00/35503 and WO
00/35505 that partially neutralized superabsorbent materials
(acidic superabsorbent materials) counteract the formation of
unpleasant odours in absorbent articles. However, acidic
superabsorbent materials absorb lower amounts of body fluid
compared to regular superabsorbent materials (in the following also
referred to as superabsorbent polymer, SAP). The absorbent articles
described in the above-mentioned WO 98/57677 may additionally
contain fluffed cellulose pulp having a pH value below 7,
preferably below 6.
[0006] Further, U.S. Pat. No. 6,852,904 describes cellulose fibers
treated with acidic odor control agents and their use in absorbent
products.
[0007] Various known odour control systems are however not
effective enough or loose their effectiveness too quickly to be
accepted by consumers of absorbent products.
[0008] Therefore, an ongoing demand exists in the art for effective
odour-control systems in absorbent articles.
[0009] From other technical areas it is further known that organic
zinc salts of unsaturated hydroxylated fatty acids such as zinc
ricinoleate are deodorizing active ingredients (see for instance DE
1792074 A1, DE 2548344 A1 and DE 3808114 A1).
[0010] It is one technical object of the present invention to
overcome deficiencies discussed above in connection with the prior
art.
[0011] It is one further technical object to provide an absorbent
article having an efficient odour control system.
[0012] It is one further technical object of the present invention
to considerably reduce or eliminate ammonia formation in absorbent
articles.
[0013] Further objects will become apparent from the following
description of the invention.
BRIEF DESCRIPTION OF THE INVENTION
[0014] The present invention relates to an absorbent article, such
as a diaper, panty diaper, panty liner, sanitary napkin or
incontinence device comprising a liquid-permeable topsheet, a
(preferably liquid-impermeable) backsheet and an absorbent core
enclosed between said liquid-permeable topsheet and said backsheet,
wherein said absorbent core comprises acidic cellulosic fibers, in
particular acidic fluff pulp fibers, having a pH value of 5.5 or
less, and an organic zinc salt, in particular the zinc salt of a
monocarboxylic acid.
[0015] The present invention also relates to acidic cellulosic
fibers having a pH of 5.5 or less characterized in that they
comprise the zinc salt of a monocarboxylic acid and their use for
odour control, especially in the aforementioned absorbent
articles.
[0016] In the present specification, the acidic cellulosic fibers
(CF) having a pH value of 5.5 or less are oftentimes simply
referred to as "acidic cellulosic fibers (CF)" and acidic fluff
pulp having a pH value of 5.5 or less as "acidic fluff pulp".
[0017] The present inventors have found that the acidic CF, in
particular fluff pulp, and organic zinc salt, in particular the
zinc salt of a monocarboxylic acid such as zinc ricinoleate,
interact in the suppression of ammonia while preferably keeping the
natural bacterial flora in the urogenital region, and they
completed the present invention based on this finding.
[0018] Without wishing to be bound by theory, the mechanism
underlying the odour reduction of the present invention is assumed
to be as follows. It was found that the ammonia which produces the
malodour in absorbent products, such as incontinence products is
formed in the following way:
Bacteria+Urea.fwdarw.NH.sub.3
[0019] In the present invention, the acidic CF, in particular fluff
pulp fibers have the function of making the environment
unfavourable for the bacteria while the organic zinc salt, e.g. the
zinc ricinoleate removes the ammonia (NH.sub.3) actually
formed.
[0020] The aim of the present invention is to develop an absorbent
article where the amount of unwanted bacteria or microorganisms,
such as ammonia-producing bacteria does not increase during
use.
DETAILED DESCRIPTION OF THE INVENTION
[0021] Throughout the specification and claims, the use of
"comprising"is intended to cover also the more restricting meanings
"essentially consisting of" and "consisting of".
[0022] As "absorbent article" we understand articles capable of
absorbing body fluids such as urine, watery feces, female secretion
or menstrual fluids. These absorbent articles include, but are not
limited to diapers, panty diapers, panty liners, sanitary napkins
or incontinence device (as used for instance for adults).
[0023] Such absorbent articles have a liquid-pervious topsheet,
which during use is facing the wearer's body. They further comprise
a (preferably liquid-impervious) backsheet, for instance a plastic
film, a plastic-coated nonwoven or a hydrophobic nonwoven and an
absorbent core enclosed between the liquid-pervious topsheet and
the backsheet.
[0024] A suitable topsheet may be manufactured from a wide range of
materials such as woven and nonwoven materials (e.g. a nonwoven web
of fibers), polymeric materials such as apertured plastic films,
e.g. apertured formed thermoplastic films and hydroformed
thermoplastic films; porous foams; reticulated foams; reticulated
thermoplastic films; and thermoplastic scrims. Suitable woven and
nonwoven materials can be comprised of natural fibers (e.g. wood or
cotton fibers), synthetic fibers (e.g. polymeric fibers such as
polyesters, polypropylene or polyethylene fibers) or from a
combination of natural and synthetic fibers. When the topsheet
comprises a nonwoven web, the web may be manufactured by a wide
number of known techniques. For example, the web may be
spun-bonded, carded, wet-laid, melt-blown, hydroentangled,
combinations of the above or the like. In accordance with the
invention, it is preferred to make use of apertured plastic films
(e.g. thermoplastic films) or nonwoven materials based on synthetic
fibers, e.g. those made from polyethylene or polypropylene homo- or
copolymers and polymer compositions based thereon.
[0025] Optionally, at least one further layer exists between the
absorbent core and the topsheet and may be made from hydrophobic
and hydrophilic web or foam materials. As "web material" we
understand coherent flat fiber-based structures of paper tissue,
woven or nonwoven type. The nonwoven material may have the same
features as described above for topsheets.
[0026] Specifically, the at least one further layer may contribute
to fluid management, for instance in the form of at least one
acquisition/distribution layer. Such structures are taught for
instance by U.S. Pat. No. 5,558,655, EP 0 640 330 A1, EP 0 631 768
A1 or WO 95/01147.
[0027] "Foam materials" are also well known in the art and for
instance described in EP 0 878 481 A1 or EP 1 217 978 A1 in the
name of the present applicant.
[0028] The absorbent core, which may be partially or totally
surrounded by a core wrap, comprises acidic cellulosic fibers, in
particular acidic fluff pulp fibers, having a pH value of 5.5 or
less.
[0029] The term "cellulosic fibers" also referred to as "CF"
relates to fibers from wood, woody plants and certain non-woody
plants and cellulose-based recycled and regenerated fibers. Woody
plants include for instance deciduous (hardwood) and coniferous
(softwood) trees. Non-woody plants include for instance cotton,
flax, esparto, grass, milkweed, straw, jute hemp and bagasse. The
cellulosic fibers are preferably "pulp fibers".
[0030] The term "pulp fibers" includes chemical pulp and mechanical
pulp fibers.
[0031] According to DIN 6730, "chemical pulp" is a fibrous material
obtained from plant raw materials from which most non-cellulose
components have been removed by chemical pulping without
substantial mechanical post-treatment. In case of chemical pulping
processes such as the sulfite or sulfate (Kraft) process, primarily
the lignin components and the hemi-cellulose components are
dissolved from the wood to varying degrees depending on the field
of application of the chemical pulp. The result is a fibrous
material consisting primarily of cellulose.
[0032] "Mechanical pulp" is the general term for fibrous materials
made of wood entirely or almost entirely by mechanical means,
optionally at increased temperatures. Mechanical pulp is subdivided
into the purely mechanical pulps (groundwood pulp and refiner
mechanical pulp) as well as mechanical pulps subjected to chemical
pretreatment: chemo-mechanical pulp (CMP), such as
chemo-thermomechanical pulp (CTMP).
[0033] The starting pulps which may be used in the present
invention may relate to primary fibrous materials (raw pulps) or to
secondary fibrous materials, whereby a secondary fibrous material
is defined as a fibrous raw material recovered from a recycling
process. The primary fibrous materials may relate both to a
chemically digested pulp and to mechanical pulp such as
thermorefiner mechanical pulp (TMP), chemothermorefiner mechanical
pulp (CTMP) or high temperature chemithermomechanical pulp
(HTCTMP). Synthetic cellulose-containing fibers can also be used.
Preference is nevertheless given to the use of pulp from plant
material, particularly wood-forming plants. Fibers of softwood
(usually originating from conifers), hardwood (usually originating
from deciduous trees) or from cotton linters can be used for
example. Fibers from esparto (alfa) grass, bagasse (cereal straw,
rice straw, bamboo, hemp), kemp fibers, flax and other woody and
cellulosic fiber sources can also be used as raw materials. The
corresponding fiber source is chosen in accordance with the desired
properties of the absorbent core, such as softness and absorption
capacity in a manner known in the art. With regard to the softness
of the products, the use of chemical raw pulps is also preferred,
whereby it is possible to use completely bleached, partially
bleached and unbleached fibers. The chemical raw pulps suitable
according to the invention include, inter alia, sulfite pulps,
kraft pulps (sulfate process), soda pulps (cooking with sodium
hydroxide), pulps from high-pressure cooking with organic solvents
(e.g. Organosolv, Organocell, Acetosolv, Alcell) and pulps from
modified processes (e.g. ASAM, Stora or Sivola process). Among the
kraft pulps, it is possible to use those which were obtained in
continuous cooking systems (MCC (modified continuous cooking), EMCC
(extended modified continuous cooking) and ITC (isothermal
cooking)). The products of discontinuous kraft processes (e.g. RDH
(rapid displacement heating), Superbatch and Enerbatch) are also
suitable as a starting product. The sulfite processes include the
acidic sulfite/bisulfite processes, bisulfite process, "neutral
sulfite semi-chemical pulping" (NSSC) process and alkaline sulfite
processes such as processes in which in addition to aqueous alkali,
sulfite and/or anthraquinone in combination with organic solvents
such as methanol were used for cooking, e.g. the so-called ASAM
process (alkali sulfite anthraquinone methanol). The major
difference between the acidic and neutral or alkaline sulfite
processes is the higher degree of delignification in acidic cooking
processes (lower kappa numbers). The NSSC process provides
semi-chemical pulps which are advantageously defibered in
downstream mechanical fibrillation before they are used according
to the invention for the purpose of oxidation. The sulfite and
kraft pulps considerably differ in terms of their fibrous material
properties. The individual fiber strengths of sulfite pulps are
usually much lower than those of kraft pulps. The mean pore width
of the swollen fibers is also greater in sulfite pulps and the
density of the cell wall is lower compared to sulfate pulps, which
simultaneously means that the cell-wall volume is greater in
sulfite pulps. For this reason, there are also obvious differences
regarding water absorption and swelling behavior of the cellulosic
fibrous materials, which must also be taken into consideration when
selecting a material for the absorbent core.
[0034] For the purpose of the present invention, general cellulosic
fibers, in particular pulp fibers as described above are also
referred to as "standard CF" or "non-acidic CF".
[0035] The cellulosic fibers to be used in the absorbent core are
preferably fluff pulp fibers. The term "fluff pulp fibers" as used
herein is well known in the art of making paper and absorbent
products. It refers to a variant of "standard CF" as described
above which is characterized by its fluffy state which can be
achieved by comminuting standard, chemical (e.g. Kraft or sulfite),
mechanical (e.g. groundwood pulp and refiner mechanical pulp) or
chemomechanical pulp (CMP), such as TMP, CTMP or HTCTMP. Preferably
chemical or chemomechanical pulp, optionally in a bleached form is
used for the preparation of fluff pulp. Fluff pulp may comprise
mainly, preferably exclusively, softwood fibers which impart the
necessary softness for use in absorbent products. Suitable wood
pulp fibers for manufacturing fluff pulp are e.g. Southern Softwood
Kraft and Northern Softwood Sulphite. There are various grades of
fluff pulps, such as debonded, also called treated, fluff pulps
which are softer than regular fluff. Main producers of fluff pulp
are Weyerhaeuser Co. and Georgia Pacific Corp. in the U.S. and
Finland-based Stora Enso Oy. For the purpose of the present
invention, general fluff pulp as described above is also referred
to as "standard fluff pulp" or "non-acidic fluff pulp". In the
following, "fluff pulp" and "fluff CF" will be used as
synonyma.
[0036] The pH value of standard CF, including standard fluff pulp
varies significantly, e.g. depending on the production method.
Generally, standard (fluff) CF have a pH of from above 5.5 to 6.5,
preferably around 6. Unlike standard (fluff) CF, the acidic (fluff)
CF for use in the present invention have a pH of 5.5 or less. For
removing bacteria, a pH value of 5.0 or less is advantageous. The
pH value of the acidic (fluff) CF is preferably 2.0 to 5.0, more
preferably 2.5 to 4.5, still more preferably 3.0 to 4.0 and most
preferably 3.2 to 3.6. The pH of CF can be measured using the
standard test Tappi T 509-02, in particular Tappi method T 509
om-02.
[0037] The acidic (fluff) CF fibers may also be admixed with
standard (fluff) CF and/or superabsorbent polymer material
(SAP).
[0038] In the corresponding absorbent core and, if applicable, each
layer thereof, the total amount of cellulosic fibers, i.e. acidic
(fluff) CF or a mixture of acidic and non-acidic (fluff) CF, is
preferably 90 to 30 wt.-%, more preferably 80 to 35 wt.-%, in
particular 70 to 40 wt.-%, for instance 70 to 50 wt.-%, based on
the weight of the entire mixture of (fluff) CF and superabsorbent
materials (without organic zinc salt). The term "(fluff) CF" is
used as abbreviation for "non-fluffed cellulosic fibers such as
non-fluffed pulp and/or fluff cellulosic fibers, i.e. fluff
pulp"
[0039] If used in admixture, the weight ratio of acidic (fluff) CF
and non-acidic (fluff) CF is not particularly restricted (e.g. 5/95
to 95/5, 10/90 to 90/10, 20/80 to 80/20). Accordingly, weight
ratios of acidic (fluff) CF/non-acidic (fluff) CF of 100/0 to 50/50
(e.g. 95/5 to 60/40, 90/10 to 70/30) can be preferably selected
depending on the properties to be achieved.
[0040] As indicated above, the absorbent core may further comprise
a superabsorbent material, which may be acidic or non-acidic.
According to one embodiment, the absorbent core contains an acidic
superabsorbent material having a pH value of 5.5 or less (measured
according to EDANA WSP 200.2), and according to a second
alternative embodiment, the absorbent core does not contain such a
material.
[0041] The total amount of the superabsorbent material may be 10 to
70 weight %, based on the weight of the core (excluding the organic
zinc salt).
[0042] The term "superabsorbent material" is well known in the art
and designates water-swellable, water-insoluble materials capable
of absorbing the multiple of their own weight in body fluids.
Preferably, the superabsorbent material is capable of absorbing at
least about 10 times its weight, preferably at least about 15 times
its weight, in particular at least about 20 times its weight in an
aqueous solution containing 0.9 wt.-% of sodium chloride (under
usual measuring conditions where the superabsorbent surface is
freely accessible to the liquid to be absorbed). To determine the
absorption capacity of the superabsorbent material, the standard
test EDANA WSP 241.2 can be used.
[0043] The acidic and non-acidic superabsorbent materials can be
distinguished by way of their pH value. While non-acidic SAPs (also
referred to as standard SAPs) have a pH which lies e.g. in a range
of 5.8 or more, acidic SAPs have a pH of 5.5 or less. Consequently,
non-acidic SAPs may increase the pH in the absorbent core
comprising acidic (fluff) CF according to the invention. Therefore,
when acidic (fluff) CF according to the invention are used along
with non-acidic SAPs, the pH of the acidic (fluff) CF used is
preferably low enough to achieve a pH of the absorbent core of 5.5
or less, preferably 5.0 or less, more preferably from 3.0 to 5.0
after wetting. The pH of the absorbent core is measured according
to the test method A described in the examples. While the pH of the
acidic (fluff) CF to achieve the above pH of the absorbent core
depends on the relative amount of acidic fluff pulp and non-acidic
SAP in the absorbent core, the acidic (fluff) CF preferably have a
pH value of 2.5 to 4.5, preferably from 3.0 to 4.0 and most
preferably from 3.2 to 3.6 in this case.
[0044] In addition to the above materials, i.e. acidic (fluff) CF
and optionally non-acidic (fluff) CF and superabsorbent material,
the absorbent core may comprise, in admixture, other absorbent
materials. Any other absorbent material that is generally
compressible, conformable, non-irritating to the wearer's skin and
capable of absorbing and retaining liquids such as urine and other
body exudates can be used. Examples of other absorbent materials to
be incorporated in the absorbent core include a wide variety of
liquid-absorbent materials commonly used in disposable diapers and
other absorbent articles such as creped cellulose wadding; melt
blown polymers, including co-form; chemically stiffened, modified
or cross-linked cellulosic fibers; tissue, including tissue wraps
and tissue laminates, absorbent foams, absorbent sponges, absorbent
gelling materials, or any other known absorbent materials or
combinations of materials.
[0045] As indicated before, the absorbent core in the absorbent
article of the invention may also contain fibers others than acidic
CF, such as acidic fluff pulp fibers. These other fibers are
preferably also capable of absorbing body liquid as is the case for
hydrophilic fibers. Most preferably the fibers are other cellulosic
fibers such as standard fluff pulp, cotton, cotton linters, rayon,
cellulose acetate and the like. The standard fluff pulp can be of
the above-described mechanical or chemical type, the chemical pulp
being preferred.
[0046] There are no specific restrictions as to the method of
producing the acidic (fluff) cellulosic fibers for use in the
present invention. According to a preferred embodiment, the acidic
(fluff) CF are obtained by treating standard CF with an acidifying
agent. If an acidifying agent is used the same differs structurally
from the organic zinc salt.
[0047] The acidifying agents for use in the present invention are
not specifically limited in kind, as long as they do not
disintegrate or decompose the standard fluff pulp being treated.
One example is SO.sub.2-water. Preferably the acidifying agent is a
suitable acid, e.g. a weak acid or a salt thereof. The use of
halogen-free non-oxidizing acids is preferred. Suitable acids are
those which when incorporated in the standard (fluff) CF will not
release any substances which may be harmful or acrid to skin. It
should be noted that the skin in the region which comes into
contact with absorbent articles is very sensitive, in infants and
adults, alike. Hence, the acid used as an acidifying agent is
preferably one that is approved of or admitted for use in food
and/or cosmetics.
[0048] Preferably the acidifying agent is selected from optionally
hydroxyl-substituted mono- and polycarboxylic acids, their salts,
and mixtures thereof. The mono- or polycarboxylic acid may be
aliphatic or aromatic. The salt is preferably an alkali metal (e.g.
K or Na) or earth alkaline metal salt (e.g. Ca or Mg). If used in
salt form, the acidifying agent, preferably the optionally
hydroxyl-substituted mono- and polycarboxylic acid is only
partially neutralized to provide acidic solutions in water.
[0049] The optionally hydroxyl-substituted monocarboxylic acid is
preferably selected from saturated or unsaturated, linear or
branched aliphatic carboxylic acids which preferably have from 1 to
18 carbon atoms, more preferably 2 to 8 carbon atoms, in particular
2 to 4 carbon atoms. The acid may be substituted by one, two or
more hydroxy groups. Examples of this monocarboxylic acid include
formic acid, acetic acid or propionic acid or lactic acid.
[0050] The optionally hydroxyl-substituted polycarboxylicacid (e.g.
diacid or triacid) may also be substituted by one, two or more
hydroxy groups. The organic (poly)acid may be an unsaturated (e.g.
mono- or diunsaturated) or saturated, linear or branched aliphatic
carboxylic acid preferably having from 2 to 18 carbon atoms, more
preferably 3 to 8 carbon atoms, e.g. 4 to 6 carbons atoms. Examples
thereof include oxalic acid, malic acid, maleic acid, malonic acid,
succinic acid, tartaric acid, citric acid or sorbic acid.
[0051] The use of optionally hydroxyl-substituted polyacids, their
salts and mixtures thereof is preferred. These polyacids are
preferably employed in a partially neutralized state and thus
capable to act as buffer. The degree of neutralization preferably
ranges from 15 to 95% of the carboxyl groups and is more preferably
30 to 90%, e.g. 50 to 80%. Such partially neutralized
polycarboxylic acids can also be provided by mixing polyacid and
the corresponding salt in the necessary molar ratio.
[0052] Generally it is preferred to select among the above mono-
and polyacids weak acids, in particular those having a pK value of
at least 1.5, more preferably at least 2, even more preferably at
least 3, e.g. 4 to 5 (for polyacids the pK1 value) measured in
water at 25.degree. C.
[0053] Most preferably, the acidifying agent is selected from
aqueous solutions of citric acid, oxalic acid, lactic acid, malic
acid, malonic acid, maleic acid, succinic acid, tartaric acid,
sorbic acid, formic acid, salts thereof, and mixtures thereof. The
most preferred acidifying agent for use in the present invention is
citric acid and its salts.
[0054] The acidic CF, in particular the acidic fluff CF can be
obtained by treating standard (fluff) CF with a solution of the
acidifying agent. The same is preferably used in a concentration of
0.5 to 10 weight-% and preferably furnishes a pH of about 2 to 6,
in particular 3 to 5. Desirably, the concentration of acidifying
agent is selected such that the weight ratio of acidifying agent(s)
to dry CF is about 1 to 20%, in particular 3 to 10%. The solution
used for the treatment is preferably aqueous although volatile
organic solvents may also be used as this facilitates the drying of
the (fluff) CF.
[0055] The treatment of the standard (fluff) CF with the solution
of the acidifying agent is achieved by combining standard (fluff)
CF with the solution of the acidifying agent (e.g. by preparing a
slurry, dipping or spraying) followed by the preferred steps of
mixing and/or drying the mixture, followed by an optional
fiberization step to break apart possibly aggregated fibers. Said
drying may be achieved by letting the treated fibers stand at
ambient air or preferably by heating, for instance to 50 to
95.degree. C. Suitable heating conditions are also disclosed in
U.S. Pat. No. 6,852,904 (col. 5, lines 30 to 53). The treatment is
preferably done by the pulp manufacturer since this obviates the
additional step of treating standard fluff pulp by the manufacturer
of the absorbent article.
[0056] As to suitable acidic (fluff) cellulosic fibers, reference
can also be made to U.S. Pat. No. 6,852,904 B2.
[0057] Very low amounts of organic zinc salts cooperate already
with acidic (fluff) CF in a very efficient odour control. A
preferred lower weight limit of organic zinc salt (calculated as
zinc) seems to be at least 10.sup.-5 g per g dry (fluff) CF. Herein
the term "dry" used in relation to acidic (fluff) CF is to be
understood such that no water has been added to the acidic SAP and
that the only water present in the acidic (fluff) CF is the
unavoidable residual water from manufacturing. For the purpose of
the present application, an acidic (fluff) CF or an absorbent core
is preferably regarded as "dry" after a circular test sample
thereof having a thickness of 5 to 6 mm, a diameter of 5 cm and
which has been compressed to a bulk of about 8-10 cm.sup.3/g has
been kept for at least one week at ambient temperature (e.g.
20.degree. C.) and a specific relative humidity, e.g. 50% RH.
[0058] More preferably, the organic zinc salt is present in amounts
of at least 5.times.10.sup.-5 g, even more preferably at least
10.sup.-4 g, even more preferably at least 5.times.10.sup.-4 g,
even more preferably at least 10.sup.-3 g per g acidic (fluff) CF.
There is no specific upper limit, even though for economic reasons,
a point may be reached where it may no longer be useful to further
increase the zinc content, for instance beyond values of 0.1 or 1 g
zinc per g acidic (fluff) CF, if this is not accompanied by an
enhanced odour suppression.
[0059] The amount of organic zinc salt in the absorbent core is
also not specifically limited. However, the amount is preferably at
least 1.times.10.sup.-5, more preferably at least
1.times.10.sup.-4, most preferably at least 5.times.10.sup.-4 g Zn
per g dry absorbent core.
[0060] There are also no specific restrictions regarding the
organic zinc salt to be used. In accordance with one embodiment of
the present invention, at least one zinc salt of an organic
carboxylic acid, in particular monocarboxyllic acid, having
preferably 2 to 30 carbon atoms, in particular 12 to 24 carbon
atoms is used. The carboxylic acid group may be attached to
aliphatic, aliphatic-aromatic, aromatic-aliphatic, alicyclic, or
aromatic residues, wherein the aliphatic chain or the alicyclic
ring(s) may be unsaturated and are optionally substituted, for
instance by hydroxy or C1 to C4 alkyl. These salts include zinc
acetate, zinc lactate, zinc ricinoleate and zinc abietate. More
preferably, the zinc salt is the zinc salt of an unsaturated
hydroxylated fatty acid having 8 to 18 carbon atoms. Although there
is no specific restriction regarding the number of unsaturated
double bonds or hydroxy groups, those fatty acids having one or two
unsaturated double bonds and one or two hydroxyl groups seem to be
preferred. The most preferred embodiment is zinc ricinoleate.
According to one embodiment of the present invention, the organic
zinc salt is activated by means of an amino acid as in TEGO.RTM.
Sorb available from Degussa.
[0061] The organic zinc salt to be used in the present invention
may also be capable of removing malodorous substances chemically
based on amines, e.g., nicotine in cigarette smoke, thiocompounds,
e.g., allicin in garlic and onions, and acids, e.g., isovaleric
acid in human sweat, and butyric acid. For instance, zinc
ricinoleate which is, e.g., marketed by Degussa under the tradename
TEGO.RTM. Sorb has the described additional odor removing effect
apart from removing ammonia.
[0062] The present invention is also not subject to any limitations
regarding the technique of incorporating the organic zinc salt into
the absorbent core. Dipping and spraying are preferred.
[0063] For instance, it is conceivable to treat the fibers [acidic
(fluff) CF, optionally in admixture with non-acidic (fluff) CF]
present in the absorbent core with a solution of the organic zinc
salt prior to, during or after admixture with other absorbent
materials such as SAP and prior to, during or after formation of
the absorbent core from said absorbent materials. [0064] According
to one preferred embodiment, acidic (fluff) cellulosic fibers,
optionally in admixture with non-acidic (fluff) CF are treated as
such, i.e. in the absence of other absorbent materials, with a
solution of the organic zinc salt. [0065] Alternatively, standard
(fluff) CF are treated simultaneously (e.g. by spraying, preparing
a slurry, or dipping) with acidifying agent and organic zinc salt.
Then, the above-mentioned, preferably aqueous solution containing
the acidifying agent also includes the organic zinc salt, in
particular the zinc salt of a monocarboxylic acid such as zinc
ricinoleate as second component. The zinc salt is preferably
contained in amounts leading to the above disclosed Zn contents per
dry acidic CF. Regarding other treatment conditions, reference can
be made to the above description of manufacturing acidic (fluff)
CF.
[0066] Both techniques can be equally carried out with the (fluff)
CF fibers (for instance by preparing a slurry, spraying or dipping
the fibers into said solution) and (fluff) CF sheets (e.g. by
dipping or spraying) as prepared by the manufacturer prior to the
delivery of the sheets to the manufacturer of the absorbent
articles. These two techniques are especially preferred since they
avoid the extra step of spraying the organic zinc salt solution
when manufacturing the absorbent article. The other optionally
present absorbent materials such as SAP are then added during or
after formation of the absorbent core.
[0067] Preferably, the cellulosic fibers and/or the SAP are
pretreated by adding a solution of the acidifying agent and organic
zinc salt, and then these are incorporated into the absorbent core
during core formation.
[0068] According to the above spraying techniques, the solution
containing the organic zinc salt, in particular zinc ricinoleate
can be sprayed on one or both sides of the absorbent core, or one
of both sides of individual layers constituting the same.
[0069] The solvent used for the solution of organic zinc salt can
be water, a preferably volatile organic solvent such as ethanol or
a mixture of water and a water-miscible organic solvent such as
ethanol. Preferably, the organic zinc solvent is present in the
solution in a relatively high concentration, preferably 1 to 30
wt.-%. The use of such concentrated solutions ensures that the
absorption capacity of the superabsorbent material is not impaired
more than necessary. Commercially available solutions of organic
zinc salts such as TEGO.RTM. Sorb A30 available from Degussa
(content of actives 30 weight %, zinc ricinoleate activated by an
amino acid) can also be employed.
[0070] The backsheet typically prevents the exudates absorbed by
the absorbent layer and contained within the article from soiling
other external articles that may contact the absorbent article,
such as bed sheets and undergarments. In preferred embodiments, the
backsheet is substantially impervious to liquids (e.g., urine) and
comprises a laminate of a nonwoven and a thin plastic film such as
a thermoplastic film having a thickness of about 0.012 mm to about
0.051 mm. Suitable backsheet films include those manufactured by
Tredegar Industries Inc. of Terre Haute, Ind. and sold under the
trade names X15306, X10962, and X10964. Other suitable backsheet
materials may include breathable materials that permit vapors to
escape from the absorbent article while still preventing exudates
from passing through the backsheet. Exemplary breathable materials
may include materials such as woven webs, nonwoven webs, composite
materials such as film-coated nonwoven webs, and microporous films.
Since there is always a trade-off between breathability and
liquid-impermeability it can be desired to provide backsheets
showing a certain, relatively minor liquid-permeability but very
high breathability values.
[0071] The above elements of an absorbent article can be assembled,
optionally together with other typical elements of absorbent
articles in a manner known in the art.
[0072] The present invention also relates to acidic cellulosic
fibers having a pH of 5.5 or less characterized in that they
comprise the zinc salt of a monocarboxylic acid. In this organic
zinc salt the monocarboxylic acid preferably has the features
stated above. Most preferably the zinc salt is zinc
ricinoleate.
[0073] Similarly the above description of cellulosic fibers, in
particular fluff pulp fibers and techniques for acidification is
fully applicable to the claimed acidic cellulosic fibers. According
to one embodiment, these are obtainable by treating cellulosic
fibers with an acidifying agent (as described above) and the zinc
salt of a monocarboxylic acid. According to another embodiment, the
acidifying agent is present in an amount of 1 to 20 weight-% based
on the dry weight of the untreated fibers.
[0074] The present invention also extends to the use of such acidic
cellulosic fibers for odour control, preferably in those areas
where bacterial control is an issue, including absorbent articles
as claimed as well wipes, such as wipes for the feminine hygiene,
baby wipes, medical wipes and wipes for cleaning bathroom
equipment, e.g. toilets; bandages; underpads; absorbent drapes;
underpants etc. Their use for odour-control in absorbent articles
of the above-described type is preferred.
[0075] The following examples and comparative examples illustrate
the present invention.
Examples
[0076] Test Methods
[0077] A) pH of Absorbent Core
[0078] The pH of the absorbent core can be measured very precisely
with the following method involving the preparation of a test
absorbent core and pH measurement using the same.
[0079] Method 1: Preparation of Absorbent Cores for Test
[0080] Absorbent cores were punched out of an absorbent core
produced in a pilot plant. A standard method of mat forming a core
was used in the production of the core in the pilot plant. The
absorbent core consisted of a homogenous mixture of acidic
(fluffed) pulp and optionally superabsorbent material. The
absorbent core was compressed to a bulk of about 8-10 cm.sup.3/g.
The size of the punched cores was 5 cm in diameter, the weight of
the same about 1.2 g.
[0081] Method 2: Measurement of pH in an Absorbent Core
[0082] An absorbent core having a diameter of approximately 50 mm
was prepared according to Method 1. A predetermined amount of Test
liquid 1 was added, 16 ml to all samples, whereafter the absorbent
core was left to swell for 30 minutes. Thereafter, pH was measured
on the liquid squeezed out of the samples using a surface
electrode, Flat-bottomed, type Single Pore Flat, Hamilton. The
results of three tests were averaged for the measurement.
[0083] Test Liquid 1 (Referred to in Method 2):
[0084] Synthetic urine containing the following substances: KCl,
NaCl, MgSO.sub.4, KH.sub.2PO.sub.4, Na.sub.2HPO.sub.4,
NH.sub.2CONH.sub.2. The pH in this composition is 6.0.+-.0.5.
[0085] The test liquid to be used is 16 ml synthetic urine (as
defined above) for each core absorbent body.
Example 1
[0086] Circular test absorbent cores having a weight of about 1.16
g and a diameter of 5 cm were punched out of an absorbent core
produced in a pilot plant. A standard method of mat forming a core
was used in the production of the core in the pilot plant. The
absorbent core consisted of a homogenous mixture of acidic fluff
pulp and superabsorbent material. The fluff pulp used was 0.69 g
Weyerhaeuser acidic fluff pulp and the superabsorbent material was
0.47 g of a superabsorber (SXM 9155, Degussa). The acidic fluff
pulp is commercially available from Weyerhaeuser under the material
description TR118 and manufactured by treating ECF Kraft pulp based
on 100% US Southern pine wood with 4% citric acid and 1% citrate as
an additive. It has a pH of 3.4.+-.0.2. The pH of the acidic fluff
pulp was measured in accordance with the standard Tappi T 509-02.
More specifically, the above pH value is the 5 minutes pulp sheet
pH based on Tappi method T 509 om-02. The absorbent core was
compressed to a bulk of about 8-10 cm.sup.3/g.
[0087] To the absorbent core 1.3 ml of a 0.5 wt.-% solution of zinc
ricinoleate (available from Degussa under the tradename TEGO.RTM.
Sorb A30, suitably diluted) was added by either dripping the
solution onto the surface (on one side) or dipping one side of the
core into the solution. The treated absorbent body was left
standing at ambient air for one week. This procedure led to a
concentration of 5.55.times.10.sup.-4 g Zn per g dry absorbent
core. Then, the absorbent body was allowed to absorb 16 ml
synthetic urine according to Method 3 as described below and
allowed to stand at room temperature.
[0088] 6 h and 8 h after the absorption of synthetic urine the
amount of ammonia developed was measured.
[0089] Five measurements were averaged as mean value. The results
are shown in Table 1.
[0090] Method 3: Measurement of Ammonia Inhibition in Absorbent
Cores
[0091] Absorbent cores were prepared in accordance with Method 1.
Test liquid 2 was prepared. Bacteria suspension of Proteus
mirabilis was cultivated in nutrient broth 30.degree. C. overnight.
The graft cultures were diluted and the bacterial count was
determined. The final culture contained approximately 10.sup.5
organisms per ml of test liquid. The absorbent core was placed in a
plastic jar and the Test liquid 2 was added to the absorbent core,
whereafter the container was incubated at 35.degree. C. 6 and 8
hours respectively, whereafter samples were taken from the
containers using a hand pump and a so called Drager-tube. The
ammonia content was obtained as a colour change on a scale graded
in ppm or volume percent.
[0092] Test Liquid 2:
[0093] Sterile synthetic urine to which has been added a growth
medium for micro-organisms. The synthetic urine contains mono- and
divalent cations and anions and urea and has been prepared in
accordance with the information in Geigy, Scientific Tables, Vol 2,
8.sup.th ed. 1981 p. 53. The growth medium for the micro-organisms
is based on information of Hook- and FSA-media for entero-bacteria.
The pH in this mixture is 6.6.
Comparative Example 1
[0094] An absorbent core was formed in the same manner as in
Example 1, with the sole exception that a treatment with a solution
of zinc ricinoleate was not carried out.
Comparative Example 2
[0095] An absorbent body was formed in the same manner as in
Example 1 with the difference that a 6 wt.-% solution of zinc
ricinoleate was used and the acidic fluff pulp was replaced with a
standard fluff pulp (NB 416 from Weyerhaeuser). This procedure led
to an amount of 6.66.times.10.sup.-3 g Zn per g dry absorbent
core.
[0096] The results in terms of ammonia formation of Example 1 and
Comparative Examples 1 and 2 are shown in the following Table
1.
TABLE-US-00001 TABLE 1 ammonia ammonia formation formation sample
description (ppm) 6 h (ppm) 8 h CEx 1 Acidic fluff pulp.sup.1 38
760 CEx 2 Zn.sup.2 + non-acidic fluff <19 270 pulp.sup.3 Ex 1
Acidic fluff pulp.sup.1 + Zn.sup.2 1 16 .sup.1Acidic fluff pulp
(Weyerhaeuser, pH 3.4) .sup.2Zinc ricinoleate .sup.3NB 416
(Weyerhaeuser)
[0097] The above experiments show that the combined use of an
acidic fluff pulp and an organic zinc salt such as zinc ricinoleate
suppresses the formation of ammonia to a very surprising extent.
Considering the fact that a human can vaguely detect the smell of
ammonium at a concentration of 150 ppm, the present invention
ensures that during use of an absorbent article, no ammonia odour
will be perceived by the wearer.
* * * * *